****NOTE: This is not a complete instructable for the time being. It goes through the construction of a keypad fully, however it does not yet fully explain or demonstrate the means to make it useful. This will change
Step 1: Understanding the Keypad
A matrix is pretty much a grid like in battleship consisting of rows and columns. each button corresponds to a certain row and column. See the first picture to help illustrate this better. On a 9 button keypad you would use 3 rows and 3 columns. The first button would make a link between Row 1 and Column 1 (R1C1) just like in battleship. 2 would be R1C2, 3 R1C3, and lets say 8 would be R3C2... the rest are illustrated on the image.
The point of this is instead of having 9 different buttons to wire up, all you would need to do is wire up 3 columns and 3 rows for significantly less wires. The real benefits come when you begin adding buttons. adding another row and column (2 wires) would add 7 buttons... see where I'm going?
Step 2: Collecting the Materials.
Aluminum Foil (tin foil... some sort of foil) *foil tape works well also
Some sort of paper or flat material (what you choose here will effect the durability. I'm using a dry erase pad for my fridge)
glue (unless you're using foil tape)
and a spacer of some sort (a few layers of paper with holes cut in them may work I'm using double sided sticky foam pads)
Laminator (COMPLETELY OPTIONAL)
Step 3: Decision Time
Step 4: Mapping Out Your Cheap "Circuit"
On these new layers we will put large black lines where we want our "Circuits" to go. See image 2 for rows and image 3 columns if you are confused. Image 4 shows what both layers turned on looks like. Starting to look familiar?
Now you need to flip one of your images vertically... or is it horizontally... see image 5 you'll get what I mean.
Go ahead and print these out for the next step.
Step 5: Faux Circuit Making Time!
Now that you have your printed out templates you can start making your circuit. Now is the time to glue down your foil where ever your rows and columns are supposed to go. Look at figure 2 for both of my circuits, yours should look somewhat like this. Also, notice how my leads go away from the keypad in an organized way to facilitate easy hook-up? Just like I planned!
*NOTE* At this point its a good idea to re-make your front design to include labels for the hookup at the end of the leads with the labels
This is just going to make it easier for you.
Step 6: Putting It All Together.
Anyways back on topic. To apply these spacers we need to make sure that there is a hole in the center of them so that the rows and columns can contact one another when they are depressed (not sad... pressed down). I kinda just tiled everything but you could use a hole punch or something to get better results. The spacers are also there to make sure other parts of our circuit do not touch each-other incidentally.
Take a look at image 1 to see all the spacers applied appropriately. Once your spacers have been applied (you may need to glue whatever you are using) you may put the other side of your keypad on top of this one (image 2). Luckily you made sure that everything was mapped out properly on your template on the computer... you did make a template didn't you?
Image 3 is the pieced together keypad.
To help my keypad enjoy a long healthy life I laminated mine. It helps provide some structural support for the paper... constant pressing can and will create depressions (again not sad) in the paper that sooner or later will cause your keypad to become ineffectively pressing that button constantly.
Image 4 would show my beautiful laminated Matrix style keypad however the laminator ate my piece of art.
Step 7: Arduino Anyone?!
Well Exciting as it may be it'll have to wait for now! The Laminator lovingly ate my keypad so until I can find the time to make another one then it'll have to wait. I WILL be coming back so do not to worry this step will come. Perhaps in the near future I will explain how to set it all up and not exactly show it off. For now here is the arduino code I was using with my prototypes for those of you who know where to go from here good luck. For the others sit tight.
***NOTE*** you will have to install the keypad library from arduino.cc